Investigations have been made about application of a metal gate electrode wherein a depletion region is not generated as a gate electrode of a transistor.
As a metal gate electrode structure, there is known a laminated structure including a silicon film and a metal film wherein the metal film is arranged as a lower portion of a gate electrode and the silicon film is arranged on the metal film.
The structure has a problem that when a resistance of the interface between the silicon film and the metal film rises, the switching speed of the transistor is lowered.
For example, a structure wherein a silicide layer is formed at the interface between a silicon film and a metal film is disclosed.
The method wherein the metal film and the silicon film are caused to react with each other to form the silicide layer, has an advantage that the silicide layer can be formed selectively only on a portion where the metal film and the silicon film contact each other.
However, there remains a problem that the surface of the metal film is oxidized so that the resistance of the gate electrode is increased, whereby a desired interfacial resistance is not obtained.